OBJECTIVE: Malignant tumors of the mesothelial lining of serous cavities, mesotheliomas, are relatively uncommon tumors for which definitive diagnostic methods are not available. I am pursuing the following protocol for establishing definitive diagnostic methods for these tumors. APPROACH AND PROGRESS: Normal mesothelial cells, present in pleural and peritoneal effusions, were cultured in RPMI 1640. The cultured cells were harvested by scrapping with a rubber policeman and washed in serum-free medium RPMI 1640. The isolated mesothelial cells were suspended in complete Freund's adjuvant and injected into rabbits. Following 3-4 booster doses of mesothelial cells suspended in saline the antiserum was collected from the rabbits and heat inactivated. The antiserum was absorbed with human red cells, liver powder and MOLT-4 cell line lymphocytes. The resulting antiserum was specific for mesothelial cells as judged by indirect immunofluorescence. The mesothelial cell-specific antiserum has been used as a diagnostic agent in differentiating mesothelioma cells from other malignant cells in serous effusions. The antiserum is being evaluated for use in immunoperoxidase staining of formalin-fixed paraffin embedded material to enchance the usefulness of the reagent. The next phase of the project calls for isolation of the mesothelial cells specific antigen and preparation of a high-titered antiserum to the antigen. An immunoassay similar to ELISA or RIA will then be established for quantitation of the antigen in effusion fluids and sera of patients. The assay is expected to measure the mesothelial cell mass and be useful in follow-up of patients with suspected or known mesotheliomas. It is possible that at a latter date the antiserum may be used in a site-directed chemotherapy regimen.